Bandpass component decimation and transmission of data in cable television digital return path

ABSTRACT

A device for and a method of decreasing the data rate of a digital return path link in a Cable Television Hybrid Fiber-Coax system (CATV system) is disclosed. At the node of the CATV system, the bandwidth of the a digital data stream representative of an analog return signal is limited to a desired frequency band. The ba 11 dwidth-limited data stream is then digitally re-sampled at a predetermined multiple of a center frequency of the frequency band. The re-sampled data stream is then separated into two data streams. Then, these separate data streams are digitally decimated to a lower data rate, interleaved and serialized for transmission to a head end of the CATV system. A reverse process reconstructs the original analog return signal&#39;s signal components within the desired frequency band at the head end.

The present application is a continuation of U.S. patent applicationSer. No. 10/218,344, entitled BANDPASS COMPONENT DECIMATION ANDTRANSMISSION OF DATA IN CABLE TELEVISION DIGITAL RETURN PATH, filed Aug.12, 2002, which claims priority to, under 35 U.S.C. §119(e), U.S.Provisional Patent Application No. 60/355,023, filed Feb. 8, 2002. Theforegoing applications are incorporated herein by reference in theirentireties.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates generally to cable television systems(CATV). More specifically, the present invention pertains to a methodand system for lowering the data rate of digital return path links for aCATV hybrid fiber coax system.

BACKGROUND OF THE INVENTION

Cable television systems (CATV) were initially deployed so that remotelylocated communities were allowed to place a receiver on a hilltop and touse coaxial cable and amplifiers to distribute received signals down tothe town that otherwise had poor signal reception. These early systemsbrought the signal down from the antennas to a “head end” and thendistributed the signals out from this point. Since the purpose was todistribute television channels throughout a community, the systems weredesigned to be one-way and did not have the capability to takeinformation back from subscribers to the head end.

Over time, it was realized that the basic system infrastructure could bemade to operate two-way with the addition of some new components.Two-way CATV was used for many years to carry back some locallygenerated video programming to the head end where it could beup-converted to a carrier frequency compatible with the normaltelevision channels.

Definitions for CATV systems today call the normal broadcast directionfrom the head end to the subscribers the “forward path” and thedirection from the subscribers back to the head end the “return path.” Agood review of much of today's existing return path technology iscontained in the book entitled Return Systems for Hybrid Fiber CoaxCable TV Networksby Donald Raskin and Dean Stoneback, herebyincorporated by reference as background information.

One innovation, which has become pervasive throughout the CATV industryover the past decade, is the introduction of fiber optics technology.Optical links have been used to break up the original tree and brancharchitecture of most CATV systems and to replace that with anarchitecture labeled Hybrid Fiber/Coax (HFC). In this approach, opticalfibers connect the head end of the system to neighborhood nodes, andthen coaxial cable is used to connect the neighborhood nodes to homes,businesses and the like in a small geographical area.

FIG. 1 shows the architecture of a HFC cable television system.Television programming and data from external sources are sent to thecustomers over the “forward path.” Television signals and data are sentfrom a head end 10 to multiple hubs 12 over optical link 11. At each hub12, data is sent to multiple nodes 14 over optical links 13. At eachnode 14, the optical signals are converted to electrical signals andsent to customers over a coaxial cable 15 in the frequency range of 55to 850 MHz.

Data or television programming from the customer to externaldestinations, also known as return signals or return data, are sent overthe “return path.” Form the customer to the node, return signals aresent over the coaxial cable 15 in the frequency range of 5 to 42 MHz. Atthe node 14, the return signals are converted to optical signals andsent to the hub 12. The hub combines signals from multiple nodes 14 andsends the combined signals to the head end 10.

FIG. 2 is a block diagram of a digital return path 100 of a prior artHFC cable television system that uses conventional return path opticalfiber links. As shown, analog return signals, which include signalsgenerated by cable modems and set top boxes, are present on the coaxialcable 102 returning from the customer. The coaxial cable 102 isterminated at a node 24 where the analog return signals are converted toa digital representation by an A/D converter 112. The digital signal isused to modulate a optical data transmitter 114 and the resultingoptical signal is sent over an optical fiber 106 to an intermediate hub12. At the intermediate hub 12, the optical signal is detected by anoptical receiver 122, and the detected digital signal is used to drive aD/A converter 124 whose output is the recovered analog return signals.These recovered analog return signals are then combined in an analogfashion with analog return signals from other nodes.

The analog return signals present on the coaxial cable 102 are typicallya collection of independent signals. In the United States, because theanalog return signals are in the frequency range of 5 to 42 MHz, thesampling rate of the A/D converter is about 100 mHz, slightly more thantwice the highest frequency in the band. A 10-bit A/D converteroperating at a sampling rate of 100 MHz is typically used for digitizingthe return signals. As a result, data will be output from the A/Dconverter 112 at a rate of about 1 Gbps. Therefore, the optical datatransmitter 114 and the optical data receiver 122 must be capable oftransmitting and receiving optical signals at a rate of 1 Gbps orhigher. The high transmission data rate results in more expensiveequipment, or a lower transmission distance, or both. The hightransmission data rate also limits the number of analog return signalsthat can be aggregated for transmission on the same optical fiber.

Accordingly, there exists a need for a method of and system fortransmitting data at a lower data rate on the return path of a HybridFiber Coaxial CATV system.

SUMMARY OF THE INVENTION

An embodiment of the present invention is a device for and a method ofdecreasing the data rate of a digital return path link in a HybridFiber-Coax Cable Television system (HFC-CATV system). In thisembodiment, at the node of the CATV system, an analog return signal isdigitized, and the bandwidth of the resulting digital data stream islimited to a desired frequency band. The bandwidth-limited data streamis re-sampled at a predetermined multiple of a center frequency of thefrequency band. Then, the re-sampled data stream is separated into twodata streams of in-phase and quadrature components at the re-samplingfrequency. Thereafter, the data streams of in-phase and the quadraturecomponents are digitally decimated to a lower data rate. Subsequently,the decimated data streams are interleaved and serialized fortransmission to a head end via optical links.

A reverse process reconstructs the original return signal's bandwidthlimited signal components at the head end of the CATV system. Morespecifically, at the head end of the CATV system, the data stream fromthe node is de-interleaved to form an in-phase data stream and aquadrature data stream. Then, the in-phase data stream and thequadrature data stream are digitally re-sampled and combined to formanother data stream. This resulting data stream is bandpass filtered andre-sampled at a higher rate to form an output data stream, which isconverted subsequently into analog form to recover an analog returnsignal.

In one embodiment, the decimated data stream has a data rate that istwice the bandwidth of the desired frequency band. If the bandwidth ofthe desired frequency band is low, low speed optical data transmittersand low speed optical data receivers can be used to transport thesignals. Because low speed optical links are inexpensive, the overallcost of the CATV system is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and aspects of the present invention will be morereadily apparent from the following description and appended claims whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows the architecture of a cable television system;

FIG. 2 is a block diagram of a cable television (CATV) digital returnpath of the prior art;

FIG. 3 is a block diagram of a CATV return path according to oneembodiment of the present invention;

FIG. 4 illustrates a relationship between spectral energy and frequencyof signals carried by a conventional CATV digital return path and adesired frequency band that is carried by a CATV digital return path ofFIG. 3;

FIG. 5 illustrates an encoder that can be used in the CATV digitalreturn path of FIG. 3;

FIG. 6 illustrates a decoder that can be used in the CATV digital returnpath of FIG. 3;

FIG. 7 depicts an example analog input waveform at 33 MHz;

FIG. 8 depicts samples of the example waveform of FIG. 7 at a samplingrate of 100 MHz;

FIG. 9 depicts the filter coefficients of a 35.3 MHz bandpass filter;

FIG. 10 depicts the filter response of the 35.3 MHz bandpass filterhaving the filter coefficients of FIG. 9;

FIG. 11 depicts samples of the example waveform of FIG. 7 at a samplingrate of 141.176 MHz;

FIG. 12 depicts an in-phase component of the waveform of FIG. 11;

FIG. 13 depicts a quadrature component of the waveform of FIG. 11;

FIG. 14 illustrates the filter coefficients of an example 3 MHz lowpassinterpolation filter;

FIG. 15 depicts the frequency response of a 3 MHz low pass interpolationfilter having the filter coefficients of FIG. 14;

FIG. 16 depicts a decimated in-phase data stream according to anembodiment of the invention;

FIG. 17 depicts a decimated quadrature data stream according to anembodiment of the invention;

FIG. 18 depicts a data stream generated by up-sampling the in-phase datastream of FIG. 16;

FIG. 19 depicts a data stream generated by up-sampling the quadraturedata stream of FIG. 17;

FIG. 20 depicts a data stream generated by combining the up-sampled datastreams of FIGS. 18 and 19;

FIG. 21 depicts a data stream generated by resampling the combined datastream of FIG. 20 at 100 mega-samples per second; and

FIG. 22 depicts an analog waveform generated using the data stream ofFIG. 21 and an analog lowpass filter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 is a block diagram depicting a CATV return path 200 according toone embodiment of the present invention. At the CATV return pathtransmitter 210, an A/D converter 112 receives an analog return signalfrom a co-axial cable 201 and generates a stream of data at a fullsampling rate (e.g., 100 MHz). A signal encoder 213 encodes the outputof the A/D converter 112 and generates another stream of data at a lowerdata rate. The low data rate output of the signal encoder 213 isprovided to the optical data transmitter 114 for transmission to a hub220 as optical signals. According to the present invention, the hub 220can be an intermediate hub or a head end hub.

At the hub 220, an optical data receiver 122 receives the opticalsignals from the transmitter 210 and converts the signals to a low datarate data stream corresponding to the one generated by the signalencoder 213. A signal decoder 223 receives and decodes the output of theoptical data receiver 122 and generates a stream of data at a fullsampling rate. The output of the decoder 223 is provided to the D/Aconverter 124 for conversion into analog signals. In this embodiment,the signal encoder 213 and signal decoder 223 enable digital data to betransmitted across the optical link at a lower rate than N*F bits persecond (where N is the number of bits and F is the sampling frequency ofthe AID converter 112). However, the entire spectrum of the analogreturn signal originally present on cable 201 is not recreated at theoutput of the hub 220. Only frequencies within a desired frequency bandof the analog return signal are recovered at the hub 220.

The analog return signal carried by the co-axial cable 201 is an analogsignal with signal components in a predefined frequency range, such as 5to 42 MHz. FIG. 4 illustrates the spectral density of the signalcomponents of a typical analog return signal. In prior art CATV systems,most or all of the signal components from 5 to 42 MHz are communicatedvia the return path to the head end. A typical sampling rate of theanalog return signal is 100 MHz, which is higher than twice the highestfrequency transmitted in the return path. In some CATV systems, users ofthe CATV return path only use specific portions of the return pathspectrum. Thus, in those systems, only those portions of the return pathspectrum carrying useful information need be transmitted from the node210 to the hub 220. Other portions of the return path spectrum can befiltered out. In one particular embodiment as shown in FIG. 4, thedesired signal is only in a portion of the return path spectrumapproximately between 34 MHz and 40 MHz with a total bandwidth ofapproximately 6 MHz. When only a specific portion of the return pathspectrum is transmitted, (e.g., the spectrum between 34 MHz and 40 MHz)the data rate of the optical link can be significantly reduced.

According to one embodiment of the present invention, the logic fortransmitting a signal that embodies a specific portion of the returnpath spectrum is implemented in the encoder 213. One implementation ofthe encoder 213 is shown in FIG. 5. As shown, a stream of A/D samples atthe Full Rate of 100 MHz is first filtered in a digital FIR (FiniteImpulse Response) band-pass interpolation filter 510 to form aband-limited data stream. The filter rate of the band-pass interpolationfilter 510 is chosen as a ratio of integers times the sample rate. Asused herein, Center Frequency of a bandpass filter refers to thefrequency approximately at the center of the frequency band to beretained. For example, if the frequency band to be retained is the bandbetween 32-38 MHz, the Center Frequency of the bandpass filter will beapproximately 35 MHz. The Center Frequency of the bandpass interpolationfilter 510, in one embodiment, is chosen to be 6/17 of the Full Rate(100 MHz), which is approximately 35.29 MHz. In the present embodiment,A/D samples enter the filter at the Full Rate (e.g., 100 MHz), andsamples are read from the multiple phase taps of band-pass interpolationfilter 510 at a rate that is a multiple (e.g., four times) of the CenterFrequency of the bandpass filter 510 to form another stream of samples.In the present discussion, it is assumed that samples are read from thebass-pass interpolation filter 510 at a rate that is four times theCenter Frequency. That is, in the present discussion, if the CenterFrequency is 35.29 MHz, then samples are read from the band-passinterpolation filter 510 at a rate of 141.176 MHz. In the presentembodiment, the data rate at which samples are read from the outputs ofthe bandpass interpolation filter 510 is set by an NCO (NumericallyControlled Oscillator) 512. In other embodiments, the rate at whichsamples are read from the outputs of the bandpass interpolation filter510 can be unequal to four times of the Center Frequency.

As an example, an analog input waveform of 33 MHz is shown in FIG. 7.When the 33 MHz analog waveform is sampled at 100 MHz, the resultingsamples are shown in FIG. 8. In this example, the coefficients of theFIR filter 510 with its Center Frequency at 35.3 MHz are shown in FIG.9, and the filter response of the FIR filter 510 is shown in FIG. 10.When the 33 MHz waveform is sampled by interpolation by the FIR filter510 at 141.176 MHz, the samples that make up a band-limited data streamare obtained. FIG. 11 depicts the band-limited data stream.

With reference again to FIG. 5, the band-limited data stream is providedto digital multipliers 514 where it is separated into two data streams,one of which carries in-phase components and the other of which carriesquadrature components. The data stream carrying the in-phase componentsis referred to as the in-phase data stream. Likewise, the data streamcarrying the quadrature components is referred to as the quadrature datastream. In the present embodiment, the separation is achieved bymultiplying the band limited data stream by the cosine and sinewaveforms whose frequency is the Center Frequency of the frequency bandto be retained. The cosine and sine waveforms, in the presentembodiment, are generated by a sin/cos generator 516 at a data rate ofthe band-limited data stream. In other words, the cosine and sinewaveforms are generated at a rate of four times the Center Frequency.Thus, in the present embodiment, the cosine waveform will include astream of +10 −10 +10 −10 . . . , and the sine waveform will include astream of 0 +10 −10 +10 −1 . . . . Digital multiplication of theband-limited data stream by the cosine waveform results in a stream ofin-phase components, and digital multiplication of the band-limited datastream by the sine waveform results in a stream of “quadrature”components. As an example, the in-phase and quadrature waveforms areillustrated in FIGS. 12 and 13. Note that zeros are not output by thedigital multipliers 514. Thus, the data rate of the in-phase data stream740 and that of the quadrature data stream 750 are approximately half ofthe data rate of the band-limited data stream 710.

In the present embodiment, the Center Frequency used by sin/cosgenerator 516 is generated by a numerically controlled oscillator (NCO)518. In other embodiments, the cosine and sine waveforms are generatedby a look up table in memory or by other computational means.

With reference again to FIG. 5, digital interpolation filters 520up-sample the in-phase and quadrature data streams such that theiroutputs can be decimated accurately by a decimation filter 525 to adesired output rate. In one embodiment, the output rate is generated byan NCO 524, and decimation is accomplished by only sampling the outputof the interpolation filters 520 at the desired output data rate. In oneembodiment, the desired output rate is at least twice the bandwidth ofthe desired frequency band. For example, if the bandwidth of the desiredfrequency band is 6 MHz, then the desired output rate is at least 12MHz.

The FIR filter coefficients for an example implementation of one of thedigital interpolation filters 520 are shown in FIG. 14. In this example,the digital interpolation filter 520 in 3 MHz lowpass interpolationfilter. The frequency response of a 3 MHz lowpass interpolation filteris shown in FIG. 15. Further, in this example, the outputs of thedigital interpolation filters 520 are decimated to a sample rate of17.647 MHz. The decimated in-phase and quadrature data streams areillustrated in FIGS. 16 and 17.

With reference still to FIG. 5, the decimated data streams generated bythe decimation filter 525 are then interleaved. The stream ofinterleaved samples is referred herein as the transport stream. The datarate of the transport stream, therefore, is the sum of the data rates ofthe decimated in-phase and quadrature streams determined by decimationfilter 525. Then, the transport stream is serialized by a SERDES circuit(not shown) and the resulting serial bit stream is used to drive theoptical data transmitter 114 for generating optical signals fortransmission to the hub 220.

Attention now turns to FIG. 6, which is a block diagram depicting animplementation of signal decoder 223 in accordance with an embodiment ofthe present invention. The signal decoder 223 is coupled to SERDEScircuits of the optical data receiver 122 to receive the transportstream generated by node 210. As described above, the transport streamconsists of interleaved in-phase and quadrature components of thetransmitted signal. At the signal decoder 223, the transport samples arefirst deinterleaved by deinterleaving logic 612 to form two separatestreams one of which is the decimated in-phase stream and the other isthe decimated quadrature stream. Then, the in-phase stream and thequadrature stream are filtered by interpolation filters 614. In oneembodiment, the interpolation filters 614 are implemented in a similarfashion as interpolation filters 520 of the signal encoder 213. FIGS. 18and 19 are the upsampled in-phase and quadrature data streams of theexample 33 MHz waveform, which are nearly the same as the waveforms ofFIGS. 12 and 13, differing only by computational errors. Here, theinterpolation filters 614 up-sample the in-phase stream and thequadrature stream such that they have a data rate at four times theCenter Frequency of the desired frequency band. In other embodiments,the interpolation filters 614 up-sample the in-phase stream and thequadrature stream to sample rates that are not equal to four times theCenter Frequency.

With reference still to FIG. 6, the signal decoder 223 includes digitalmultipliers 618, 619 and sin/cos generator 620 for generating sine andcosine waveforms. As shown, the sin/cos generator 620 receives theCenter Frequency from the NCO 622 and generates cosine and sinewaveforms at the Center Frequency. Note that the cosine and sinewaveforms, in the present embodiment, are generated at a data rate fourtimes the Center Frequency. Thus, in the present embodiment, the cosinewaveform will include a stream of +10 −10 +10 −10 . . . , and the sinewaveform will include a stream of 0 +10 −10 +10 −1 . . . . The in-phasestream is multiplied by the cosine waveform and the quadrature stream ismultiplied by the sine waveform. Digital multiplication of the stream inphase by the cosine waveform results in a stream of values withalternating zeros, and digital multiplication of the quadrature streamby the sine waveform results in another stream of values withalternating zeros.

The outputs of the digital multipliers 618, 619 are added in by digitaladder 624 to generate yet another data stream whose data rate is fourtimes the Center Frequency. The upsampled and combined samples of theexample 33 MHz waveform are shown in FIG. 20. The output of the digitaladder 624 is processed by a bandpass interpolation filter 626, which isconstructed similarly to the bandpass interpolation filter 510. Theoutput of the bandpass interpolation filter 626 is decimated to anoutput data rate. In the present embodiment, the output data rate, whichis defined by NCO 628, is the Full Rate (e.g., 100 MHz). The 100mega-sample per second resampled output of the bandpass filter is shownin FIG. 21 for the example 33 MHz waveform. The digital samples outputby the signal decoder 223 are sent to the D/A converter 124 to beconverted to an analog signal. The analog signal thus recovered willhave signal components within the desired frequency band. For theexample 33 MHz waveform, the output of the D/A converter with an analoglow pass filter is the recovered analog wave form of FIG. 22.

While the present invention has been described with reference to a fewspecific embodiments, the description is illustrative of the invention,and is not to be construed as limiting the invention. Variousmodifications may occur to those skilled in the art without departingfrom the true spirit and scope of the invention. For instance, inanother embodiment, the desired frequency band transmitted encompassesthe full bandwidth of the input signal. That is, for a frequency band tobe transmitted is 5 MHz to 42 MHz, and the Center Frequency isapproximately 22.5 MHz. In other embodiments, the Center Frequency canbe any frequency that is below one half of the frequency of the inputdata stream.

It should also be noted that some embodiments of the present inventiondescribed above can be implemented by hardware logic (e.g., FieldProgrammable Gate Array(s)). However, a person skilled in the art wouldrealize that portions of the present invention can be implemented ascomputer executable programs executable by a digital signal processor.

1. A signal decoder for use in a cable television return path and configured to receive a first stream of digital samples that include first digital samples interleaved with second digital samples of signals within a predetermined frequency band, the signal decoder comprising: a deinterleaver configured to deinterleave the first stream of digital samples and generate a stream of first digital samples and a stream of second digital samples; interpolation filters configured to filter the stream of first digital samples and the stream of second digital samples; up-sampling logic configured to up-sample the outputs of the interpolation filters to form a first up-sampled stream and a second up-sampled stream of digital samples, the first up-sampled stream and the second up-sampled stream both having a data rate that is a predetermined multiple of a center frequency of the predetermined frequency band; combining logic configured to combine the first up-sampled stream and the second up-sampled stream to generate a combined stream of digital samples; and a bandpass interpolation filter configured to filter the combined stream to generate an output stream of digital samples at an output data rate higher than that of the first stream of digital samples.
 2. The signal decoder of claim 1, wherein the data rate of the first up-sampled stream and the second up-sampled stream is four times the center frequency of the predetermined frequency band.
 3. The signal encoder of claim 1, wherein the up-sampling logic comprises a numerically controlled oscillator coupled to multiple phase taps of the bandpass interpolation filter.
 4. The signal encoder of claim 1, wherein the combining logic comprises: a waveform generator configured to generate a first waveform and a second waveform that is 90° out-of-phase of the first waveform, the first waveform and the second waveform both having the center frequency and having a data rate four times of the center frequency; a first digital multiplier configured to multiply the stream of first digital samples with the first waveform; a second digital multiplier configured to multiply the stream of second digital samples with the second waveform; and an adder configured to add the outputs of the first digital multiplier and the second digital multiplier to produce the combined stream of digital samples.
 5. A device for use in a cable television return path, comprising: an optical data receiver configured to receive an optical signal from an optical medium and to convert the optical signal to a serial bit stream; a deserializer configured to convert serial bit stream into a first stream of digital samples each having a plurality of bits; a deinterleaver configured to deinterleave the first stream of digital samples and generate a stream of first digital samples and a stream of second digital samples; interpolation filters configured to filter the stream of first digital samples and the stream of second digital samples; up-sampling logic configured to up-sample the outputs of the interpolation filters to form a first up-sampled stream and a second up-sampled stream of digital samples, the first up-sampled stream and the second up-sampled stream both b.aving a data rate that is a predetermined multiple of a center frequency of the predetermined frequency band; combining logic configured to combine the first up-sampled stream and the second up-sampled stream to generate a combined stream of digital samples; a bandpass interpolation filter configured to filter the combined stream to generate an output stream of digital samples at an output data rate higher than that of the first stream of digital samples; and a digital-to-analog converter configured to convert the output stream of digital samples to an analog signal.
 6. The signal decoder of claim 5, wherein the data rate of the first up-sampled stream and the second up-sampled stream is four times the center frequency of the predetermined frequency band.
 7. The signal encoder of claim 5, wherein the up-sampling logic comprises a numerically controlled oscillator coupled to multiple phase taps of the bandpass interpolation filter.
 8. The signal encoder of claim 5, wherein the combining logic comprises: a waveform generator configured to generate a first waveform and a second waveform that is 90° out-of-phase of the first waveform, the first waveform and the second waveform both having the center frequency and having a data rate four times of the center frequency; a first digital multiplier configured to multiply the stream of first digital samples with the first waveform; a second digital multiplier configured to multiply the stream of second digital samples with the second waveform; and an adder configured to add the outputs of the first digital multiplier and the second digital multiplier to produce the combined stream of digital samples.
 9. A signal encoder for use in a cable television return path and configured to receive a first stream of digital samples from an analog-to-digital converter, the first stream of digital samples being representative of an analog return path signal. that is sampled at a first data rate, the signal encoder comprising: a bandpass interpolation filter configured to receive the first stream of digital samples and to substantially remove signals outside of a predetermined frequency band; up-sampling logic configured to up-sample outputs of the bandpass interpolation filter and to generate a second stream of digital samples at a second data rate; separation logic configured to separate the second stream of digital samples into a third stream of digital samples and a fourth stream of digital samples; interpolation filters configured to filter the third stream and the fourth stream; and down-sampling logic configured to select digital samples from the outputs of the interpolation filters and to interleave the selected digital samples to form a fifth stream of digital samples, the fifth stream having a third data rate that is lower than the first data rate.
 10. A signal decoder for use in a cable television return path and configured to receive a first stream of digital samples that include first digital samples interleaved with second digital samples of signals within a predetermined frequency band, the signal decoder comprising: a deinterleaver configured to deinterleave the first stream of digital samples and generate a stream of first digital samples and a stream of second digital samples; interpolation filters configured to filter the stream of first digital samples and the stream of second digital samples; up-sampling logic configured to up-sample the outputs of the interpolation filters to form a first up-sampled stream and a second up-sampled stream of digital samples; combining logic configured to combine the first up-sampled stream and the second up-sampled stream to generate a combined stream of digital samples; and a bandpass interpolation filter configured to filter the combined stream to generate an output stream of digital samples at an output data rate higher than that of the first stream of digital samples. 